1. Field of the Invention
The present invention relates to an image processing apparatus that processes image data, and an image forming apparatus that reads an image and forms an image on a medium.
2. Description of the Related Art
A high-speed serial interface called a Peripheral Component Interconnect (PCI) Express (registered trademark) corresponding to a successor standard of the PCI bus system is proposed (for example, Interface, July 2003, “Outline of the PCI Express Standard” by Takashi Satomi).
FIG. 22 is a schematic diagram for explaining flows of image data in a conventional digital copying machine including special-purpose and general-purpose buses. The flows of image data are indicated by arrows.
In a digital copying machine 201 shown in FIG. 22, image data read by an image input device 202 is temporarily stored in a memory 203 and is output to a printer engine 204 to form an image. The digital copying machine 201 has a function of compression-encoding the image data stored in the memory 203 with a compressor 208, and of storing the image data in the memory 203 again or in a hard disk (HD) 205. An input/output area 206 of the memory 203 is a storage area that temporarily stores the image data read by the image input device 202. A storage area 207 is a storage area that stores the image data compression-encoded by the compressor 208. Input of data to and output of data from the memory 203 are arbitrated by an arbiter 209 and performed by a memory bus 210.
However, in such a conventional system, as described above, image data always passes through the memory bus 210 when the image data is processed. Thus, a shortage of bands of the memory bus 210 can occur. For example, it is assumed that a data transfer rate from the image input device 202 to the memory 203 is 15 MBytes/sec, a data transfer rate from the memory 203 to the printer engine 204 is 20 MBytes/sec, a data transfer rate from the memory 203 to the compressor 208 is 25 MBytes/sec, a data transfer rate from the compressor 208 to the memory 203 is 25 MBytes/sec, and a data transfer rate from the memory 203 to the HDD 205 is 50 MBytes/sec. Start times and end times of the respective data transfers and a sum of the data transfer rates of the memory bus 210 in this case are shown in FIG. 23. It is assumed that the start time and the end time of the data transfer from the image input device 202 to the memory 203 are 0 second and 0.60 second, respectively, the start time and the end time of the data transfer of the image data on the memory 203 to the printer engine 204 are 0.36 second and 0.81 second, respectively, the start time and the end time of the data transfer of the image data on the memory 203 to the compressor 208 are 0.48 second and 0.66 second, respectively, the start time and the end time of the data transfer from the compressor 208 to the memory 203 are 0.48 second and 0.66 second, and the start time and the end time of the data transfer of the compression-encoded data on the memory 203 to the HDD 205 are 0.57 second and 0.75 second respectively. Then, a data transfer at a rate of 135 MBytes/sec occurs in a period between 0.57 second and 0.60 second when the respective data transfers overlap one another.